The relative contributions of cannabis and alcohol use to educational outcomes are unclear. This research examined the extent to which adolescent cannabis or alcohol use predicts educational attainment in emerging adulthood.

It was found that teenagers who smoke cannabis at least once a week are less likely to finish school, enrol in university or obtain a degree, challenging the notion that alcohol might be more harmful than cannabis.

Using data from three longitudinal studies from a total of of 3,600 young people from Australia and New Zealand, the study found that lower educational outcomes for those who smoked cannabis before the age of 17.

Just under half (47%) of those who used at least weekly failed to complete high school, 69% did not enrol in university and 88% did not obtain a degree.

These teenagers had odds of not progressing with formal education that were between 1.6 to 2 times higher than cannabis non-users.

The magnitude of the effect of cannabis use on educational attainment remained significant even after taking into account 53 individual, parental and peer factors which might otherwise explain the association.

In contrast, after taking these factors into account the study found no statistically significant association between early alcohol use and educational attainment.

These findings are important to the debate about the relative harms of cannabis and alcohol use and identify an important target population for preventive intervention.